The surface structure of 6H-SiC(0001)Si prepared by heat treatment has been studied using Auger electron spectroscopy (AES) and scanning tunnelling microscopy in ultra-high vacuum (UHV-STM). The C(KLL) Auger signal increased in comparison with Si(LVV) for increasing heating temperature. 6 X 6, 3 X 3 and root 3 X root 3 reconstructions were observed above 1100 degrees C by STM, but only 6 X 6 domains exist at the highest temperature (1250 degrees C). The 6 X 6 and 3 X 3 reconstructions can be explained by the structure of a graphitic layer on the SiC surface and by the 3 X 3 DAS model, respectively.